This invention relates to air-driable alkyd resins and a process for their preparation.
Air-driable alkyd resins are widely used in paints and similar coating compositions because upon exposure to air the resins form a tough coating which is not easily chipped or broken. The conventional process for producing alkyd resins comprises heating an alcohol containing at least three hydroxyl groups (typically glycerol), monobasic fatty acids and dibasic acids, such as phthalic acid, at high temperatures, typically about 230.degree. to 250.degree. C. Large quantities of energy are consumed in maintaining for several hours the reactant at the elevated temperature required for the reaction in order to drive off the by-product water formed. Moreover, during the protracted heating period, substantial amounts of side-products are formed during the reaction, and these side-products frequently produce an undesirable color in the resin, which may cause difficulty where the resin is intended for use in a white or other light-colored paint. Removal of the side-products and of any color developed is difficult.
The conventional process may also provide a resin having a wide range of molecular weights. This is undesirable since the presence of a wide range of molecular weights of polymerized material causes difficulty in obtaining proper coating characteristics.
The alkyd resin produced by these conventional processes is used with organic solvents with pigments and drying agents to prepare the final paint or other coating material.
There is thus a need for a process for preparing alkyd resins which employs lower temperatures than the conventional process, thereby saving energy and avoiding the formation of colored by-products in the alkyd resin. Furthermore, it is desirable that such a process be completed in a shorter reaction time than the conventional process since this would allow additional energy savings and more efficient use of plant. It is also desirable that such a process produce a resin having a narrower range of molecular weights than the prior art processes. The subject invention provides such a process.